Generally, during interlacing for interpolating pixels to improve the resolution of a three element CCD camera, a R channel CCD (charge coupled device) and B channel CCD are constructed with a spatial difference in a video camera provided with CCDs respectively for red, green and blue color. The conventional method and apparatus for and interlacement of the interpolating pixels are as shown in FIGS. 1 and 2.
As shown in FIG. 2A, R beams among the input beams through a lens 1 and a prism 2 pass through an R channel CCD 3, and then, are converted to electrical signals at an R channel CCD signal pickup stage 11 of a CCD pickup circuit 10 of FIG. 1, and are output. Signal R1 is applied to a pre-amplifier 40 after passing through a first correlated dual sample-hold stage 21 of a correlated dual sample-hold circuit 20, which detects and removes dark current occurring during the feed through period.
Meanwhile, G beams are converted to electrical signals at a G channel CCD signal pickup stage 12, and then, the signals are delayed by 1/2 pitch by a 1/2-pitch delaying circuit 30 using sample-hold processing. Then, the signals are applied to a second correlated dual sample-hold stage 22, and then, noises are removed from the signals by the stage 22, before such formed signals G2 are applied to the pre-amplifier 40.
Meanwhile, B beams are converted to electrical signals at a B channel CCD signal pickup stage 13, and the signals thus formed pass through a third correlated dual sample-hold stage 23. During the passage, dark current is removed from the signals to form signals B2, and then, the signals B2 are applied into the pre-amplifier 40.
The signals R2, G2 and B2 applied to the pre-amplifier 40 are fed to pass low pass filters and subjected to gain amplifications. Then, the signals pass through a video processor and encoder circuit 50 before being provided in the form of composite video signals Vo, where the G signals G.sub.1 perform a function as shown in FIG. 2 in the 1/2-pitch delaying circuit 30.
FIG. 2B shows an example of a 12 pixel CCD element, in which G channel CCD 4 is delayed by 1/2 pitch in the horizontal direction. If the signals R2, G2 and B2, in which the G side is delayed, are mixed together, they constitute a signal arrangement as shown in FIG. 2C.
Thus, when the pixels being interpolated are interlaced by 1/2 pitch, the sample and hold response Rf is as follows. ##EQU1## where .chi. represents a delayed angle, and M(j.omega.) represents a phase of a complex number seen during the sample and hold processing.
If the Formula (1) is applied to a 1/2-pitch interlacing method, the following formula is obtained. ##EQU2##
In the above formula, fc is a Nyquist Frequency which is obtained by carrying out sampling at a frequency over twice the maximum frequency of the base band signals to be samples. The frequency fc will be termed sampling frequency below. Frequency is a maximum frequency of the base band signals and has a relationship with fc in which fo=fc/2. Further, .DELTA.T is a holding time, and Tc is the period of one clock cycle, that is, 1/fc. If the above variables are substituted into Formula (2), the following formula is obtained. ##EQU3##
That is, sin .pi./4=sin 45.degree.=1/2, and therefore its resolution m.sub.1 is defined as follows. ##EQU4##
In the above formula, m represents the resolution in the case where the 1/2-pitch interlacing method is not employed. The resolution m.sub.1 is increased by 2 times at the maximum as shown in Formula 4 in the case where the 1/2-pitch interlacing method is employed.
Meanwhile, the magnitude of the upper frequency signals, which appears upon performing the sampling, is as shown in FIG. 6. As is well known, luminance signals Y can be expressed as follows. EQU Y=0.3R+0.59G+0.11B (5)
Therefore, the following values can be obtained, because the G channel is delayed by 1/2 pitch as compared with the R and G channels. That is, Y.sub.R.B =0.41=0.3+0.11. Y.sub.G =0.59. Therefore, the upper frequency signal components can be expressed as shown in FIG. 6, and it can not be removed completely in the vector product generated by the values of Y.sub.R.B and Y.sub.G.